|galactic coordinate system |
The coordinate system in which a celestial object's position on the celestial sphere is described in relation to the structure of the Milky Way galaxy. ◇ An object's galactic longitude is measured along the galactic equator, a great circle on the celestial sphere that follows the band of the Milky Way. The galactic equator, also called the galactic circle, is inclined at an angle of approximately 62° to the celestial equator; distances are measured along it beginning at a point in the constellation Sagittarius lying in the direction of the Milky Way's nucleus. The galactic poles are the two points where a perpendicular line through the middle of the plane of the galactic equator intersect the celestial sphere. ◇ An object's galactic latitude is measured in degrees north or south of the galactic equator toward the galactic poles.